At least two people are dead, and hundreds injured, after Ukraine's long-running peaceful anti-government street demonstrations erupted in unprecedented violence this week, and the protest movement appeared to split irrevocably between moderates and revolution-bent radicals.

Ukrainian riot police reportedly began clearing away barricades in central Kiev Wednesday afternoon following a night of bloody clashes between police and a radical contingent of protesters near the country's parliament, which saw the first fatalities since the demonstrations began last November. One man was shot – allegedly by police, though they deny using live ammunition – another fell to his death after climbing a stadium wall, and a third was reported dead of a bullet wound in a Kiev hospital.

The vast majority of protesters remain in the the city's central square, known as Independence Square or the Maidan, peacefully occupying the space as they have for two months. But authorities now say they are in violation of a new law banning all public protests, passed by parliament last week, which came into effect today.

Most of the violence has unfolded a few hundred yards away, where a few hundred ultra-nationalist protesters who call themselves the "Right Sector" have battled openly with police, using iron bars, stones, and Molotov cocktails. On Tuesday night they even deployed a medieval catapult, built according to instructions downloaded from the Internet, which managed to hurl only a few projectiles before being destroyed by police.

"I express my great regret at the loss of lives in the conflict provoked by [political] extremists," Mr. Yanukovych said. "It’s still not too late to stop and settle the conflict peacefully. Once again I urge the opposition to sit at the negotiating table and stop the confrontation," he said.

The crisis has blown up unexpectedly and, experts say, now that Ukraine's long-standing taboo against political violence lies in tatters, there is no predicting what may happen next. Russian Foreign Minister Sergei Lavrov warned Tuesday that the situation in Ukraine is "getting out of control" and blamed Western leaders for encouraging protesters who are engaged in acts of street violence that would not be acceptable in any European country. "It seems that someone is interested in this chaos," Mr. Lavrov suggested.

For their part, moderate Ukrainian protest leaders blame Moscow for orchestrating the anti-Europe policies of President Viktor Yanukovych, and some even suggest that Russian secret services might be behind the provocative street violence of the "Right Sector."

"This was all prompted by the Kremlin," says Pavel Movchan, a parliamentary deputy with the BYuT party, led by jailed opposition leader Yulia Tymoshenko. "The whole program was worked out in Moscow, and it's now being realized in practice. ... The danger now is that Ukraine can become uncontrollable. It might possibly lead to the break-up of Ukraine. But there is a high degree of resistance in all strata of Ukrainian society, particularly among the youth."

Barely two weeks ago, the protests appeared to be petering out amid bitter winter cold and news that Russian President Vladimir Putin had relieved Ukraine's desperate financial problems by granting Mr. Yanukovych a cash loan of $15 billion.

But the ham-handed anti-protest law passed by a narrow pro-Yanukovych majority in the parliament, which goes against Ukraine's political traditions, appears to have reinvigorated protests on the Maidan, which swelled to over 100,000 people on Sunday. "This is a battle for democracy. Ukrainian citizens are demanding that the authorities listen," says Olga Bodnar, an opposition parliamentary deputy. "Unfortunately, two people are dead. Real bullets are flying now."

Sergei Strokan, foreign affairs columnist with the Moscow daily Kommersant, says that the consequences of the violence – whoever may be provoking it – may be catastrophic.

"There has always been a consensus, across Ukraine's political spectrum, that a Ukrainian quarrel is different from a Syrian, or even a Russian one. After all, this is a country that went through the 'Orange Revolution' in 2004, without a single instance of violence," he says.

"There are now different agendas in play. The opposition has split between moderates and radicals, and the radicals are already rejecting the authority of moderate opposition leaders such as Vitali Klitschko, Yuri Lutsenko, and Arseny Yatsenyuk," Mr. Strokan says. "The moderates might be willing to hammer out a deal with Yanukovych, especially if it would lead to early elections. The radicals are apparently not interested at all in talking with the government, or compromising with it, but want to overthrow it. Yanukovych would like to restore order, but he no longer has any idea how to do this. This situation is fraught with danger."

Some experts say the violence is increasing public support for the radicals, and the longer it goes on, the greater the danger that Ukraine's delicate political balance will be permanently destabilized.

"Both sides are attacking each other now. The police are using firearms and rubber bullets, including some kinds of weapons that are prohibited in Ukraine. The radicals are using Molotov cocktails and paving stones. They just go on battering each other," says Alexander Chekmishev, deputy director of the journalism department at Kiev State University. "The authorities refuse to make any compromises. They talk about wanting dialogue, but they don't actually agree to do it."

Mr. Chekmishev adds that the potential for lethal violence in Kiev is high, thanks to a prevalence of guns. "Bear in mind that there are lots of firearms in Kiev in private hands; there are probably about 8 private guns for every Berkut [riot unit] policeman," he says.

Mikhail Pogrebinsky, director of the independent Kiev Center of Political and Conflict Studies, says the radicals are now driving events.

"The opposition is now effectively calling on everyone to come out and take part in the revolution. The leaders on the Maidan are now actually solidarizing with the most aggressive radicals who go out and physically attack the police, and then they blame the authorities for whatever happens," he says. "There is no space for dialogue under circumstances like these."